Tappet



JPN

umso, 1924. 1

' M. M. WILCOX TAPPET Filed May 31 1924 v au 004% .g

l ext/tonnes.,

Patented Dec. 30, 1924s MERRL'L IVI. 'W`IIJCOX5` OF SAGINAW, MICHIGAN.

TAPPET.

Application filed May 31, 1.924.l Serial No. 716,979.

To all whom, z't'ymoy concern:

Be it known that l,` MERRILLM. VVILooX, a citizen of the United States, residing at `Saginaw, in the county of Saginaw and State of Michigan, have invented certain new and useful Improvements in Tappet-s; and ll do hereby decl-are the following to be a full, clear, and exact description of, the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to valve tappets and pertains more particularly to certain improvements in the construction of valve tappets such as are commonly used in the engines of automobiles, aeroplanes and the like. vMy improvement relates more specifically to tappets comprising a tubularbody and acam-contacting head of hardened material, the head formed with an elongated cylindrical shank received within the tubular body and secured thereto by spot weldne In practice the tubular body is usually of `wrought*metal such as steel, and the camcontacting head is of cast iron and has a working face hardened by chilling.

Tappets of this character are described and claimed in my Paent No. 1,470,041, issued October 9, 1923, to which reference may be had.

My present invention has for its objects to increase the wearing qualities and the working life of the tubular body, which in the operation of the engine slides lengthwise in a bearing. After long continued use the tubular bodies or stems of tappets show the first signs of wear at places near the two ends of the stem, doubtless caused by the sidewise thrust of the actuating cam. Extreme hardness is, therefore, essential at areas near the ends of the stem. y

Heretofore the spot welding Voper-ation has, by reason of heat'unavoidably conducted from the weld, reduced the hardness previously imparted tothe lower part of the stem. It is a purpose of `my invention to enable the stem to retain as nearly as possible the full degre of its initial hardness.

lat the edges of the spot weld and thereby does away with the formation of sliver-s at the edge of the welded area. Such welding sliv'ers or projections are of extreme hardness, being considerably harder than the heat-treated and hardened cylindrical surface of the tappet stein. These extra hard projections on the cylindrical wall of the tappet are a serious disadvantage in manufacture.

Extreme accuracy is required with respect to the diameter of the finished tappet stem, which is usually required to be of uniform diameter throughout its length within tolerances of two tenths of one thousandth of an inch. The tappets must fit in the engine brackets so closely that even when ground to the above degree of accuracy they are inserted in the respective bearings in the tappet bracket of the engine by selection, the tappet best suited for each hole being picked out by trial. If the spot weld ing is done on the original diameter of the stem without the groove or chamber areas, and the welding flash produces a hardened projection, then in the grinding of the tappet the grinding wheel becomes worn unevenly on account of the extra hard flash weld projections.l and after a time it has been found that the tappet diameters are not sufciently accurate to comply with the requirements. Sometimes around the area in which the flashing has occurred the finished stem diameter will be one-tenth of one thousandth of an inch larger than at any other diameterl in its length. Such tappets frequently have to be rejected.

By spot welding in the groove, or in the equivalent chambers, the grinding wheel does not come in contact with hardened flash projection and consequently not worn unevenly and will produce uniform grinding for an indefinite length ot' time. 100

The groove also serves as a gauge to indi? i cate to the operator when the Welding contact points have become blunt and require .re-sharpening.

A still further object of my invention is to provide a circumferential lubricating channel on the tappet stem intermediate the two hardened extremities of the stem.

lilith the foregoing and certain other objects in view which will appear later in the specifications my invention comprises the devices described and claimed and the equivalents thereof.

In the drawings Fig. 1 is a side view of a tappet embodying my improvement, the hardened areas indicated by stippling and the extent of travel of the tappet by dotted l Fig. 2 'isa cross section on the line .2 2

of Fig. l. H y

. Fig. 3 is a side view of a spot welded tubular body indicating the flashing out actionwhen the welding groove is not used. Fig.` t is a similar view showing the groove and welding spots therein.

Fig. 5 is a side view of a tappet stem showing the spotyweld applied to a thin wall formed` by milling the spots on the stem instead of on the continuous groove.

As is clearly` shown in the drawings, 1 is ythe tappet body and 2 is the head Which is usually formed of a separate piece of'metal such` as cast iron,r and hardened either by heat treatment or by chilling. 3 is a flange, the surface of which is preferably hardened to contact with the engine cam 4, as shown rin Fig. l. An elongated .axially projecting cylindrical `shank 5 is formed on the head 2 and is accurately fitted within the tubular body l, `to which it is secured by spot weldinfr.

In practice the tubular body l is independently hardened by heat treatment, the

hardness being about seventy points by they scleroscope. To aii'eet the Welding without appreclably decreasing the hardness of the lower part of the stein is, as above stated,

one of the objects of my improvement.

Referring te Fig. 3, a stem is shown having spot welds applied to its outer surface as has been the practice heretofore..l These spots are lindicated at 6 and the edges of the spot, as at 7, are usually found to have flashed out, causing hardened projections or slivers on the outer working surface of ythe tappet stem, as previously described.

In my present invention I form a groove or chamber 8 by machining the stem l before it is hardened, so as to produce a thinner wall Zr-see Fig. Q-as compared with the'original thickness T. The spot weld is applied in this groove, as indicated in Fig.

t, instead of through the original thickness of the tappet as heretofore.

in Fig. 3, requires more time and more heat than is requiredto do equally effective Welding through the inner Wall t, asindicated in Fig. ll. Thus not only is time saved in the Welding operation, but less heat is conducted to the loWerpart of the hardened tubular stem and consequently its'hardness is reduced to a lesser extent than heretofore.

In practice the spot vwelding operation when applied through the full thickness yT of the tappet stem Wall as shown in Fig. 3, heats the lower part ofthe stein to such an r extent as to reduce its indicated hardnessv Afrom about seventy points bythescleroscope to about forty points, but when the Weld is applied to the thinner metal t, forming the wall of groove 8, the lower part of the stem is not heated so much and the hardness is only reduced'about one-third as much, or to about sixty points. This enables the lower end of the stem `to be ,keptl hard enough to resist wearthat could not formerly' be resisted.

The groove 8 or the equivalent chambered areas also serves as an oilfcarryingor lubricatingfchannel to keep the middle part of rthe length of thestem properly lubricated.

By means above described I have produced a simple and relatively inexpensive, yet kstrong and durable tappet having the ends of its stem, where the greatest wear occurs, of extreme hardness: The circumferential groove by reducing the time required for welding and the amount of heat required to produce a? proper weld, imparts to the completed tappet advantages that have not heretofore been present in two piece tappets of the class described.

Having thus describedv my invention,l

what I claim and desire to secure by Letters Patent is:

l. In a tappet comprising a tubular body and a cam-contacting head formed with an elongated.cylindrical shank received within said body, an external circumferential groove formed in said tubular body, the Wall of metal of reduced thickness comprising the bottom of said groove spot-Welded to said shank.

2. Ina tappet comprisinga tubular body vof hardened metal and a cardeontacting` ltlietubnlar Wall of said body adjacent said body.

head formed with an elongated cylindrical ing and consequent reduction of hardness shank received Within said body, a part of of adjacent parts of sind hardened tubular shank externally chambered to provide an In testimony Where-of, I aiix my signuarea oi reduced thickness, said Wall spotture.

Welded to said shank in said area of reduced thickness, whereby to prevent excessive heat- MERRILL M. WILCOX. 

